Induced flow by coiled tubing gas injection in depleted gas wells: Modeling and applications

• Presenting the technology of using coiled tubing (CT) gas injection to obtain induced self-flow in depleted gas wells.
• The pressure distribution in the annulus is calculated by numerical modeling based on gas–liquid two-phase flow theories.
• The effects of injection depth, injection rate, CT size, wellhead back pressure and well deviation on CT gas lifting are investigated.
• Two field cases are chosen to demonstrate this technology and verify the modeling results.

Induced flow after completion is one of the challenges that hinder the development efficiency for depleted offshore gas reservoirs. Coiled tubing (CT) gas injection has many advantages in inducing the wells to self-flow. The critical conditions of induced self-flow are analyzed. And the pressure distribution in the annulus between the oil tubing and CT is calculated by numerical modeling based on gas–liquid two-phase flow theories. The effects of gas injection depth, injection rate, CT size, wellhead back pressure, and well deviation angle on the results of induced self-flow are investigated. Numerical modeling results indicate that the pressure drop caused by gas injection decreases significantly as the injection depth decreases, and as the wellhead back pressure and the well deviation angle (especially for high angles, >60°) increases. Within the range of injection rates commonly used for CT gas injection, CT size and injection rate show little influence on the pressure drop. Therefore, injection depth and wellhead back pressure are key factors controlling the results of the induced flow treatment. For horizontal wells and high deviated wells, it is better to use a deeper injection depth and/or lower wellhead back pressure, which benefits the successful induced flow.

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